Insulating windows and window-pane units generally comprise an inner glass pane, an outer glass pane and a frame in which the panes are sealingly received and serving to space these panes apart so that the panes define a gas-filled space between them.
One or both of the panes may be formed by a single glass sheet or a plurality of glass sheets with evacuated or gas-filled spaces and the entire assembly may be sealed along its periphery and received in a sash or other assembly for insertion into a window opening or can be built directly into the window opening.
It is known (see German patent document No. 20 31 576, FIG. 2) to provide a yieldable membrane between at least one of these panes and the remainder of the frame. This membrane is resilient, i.e. resists displacement by the development of a spring or restoring force and may be provided in the form of a spring metal strip with harmonica-like folds allowing relative displacement of the panes.
The spring strip serves to secure the pane to which it is connected in the structure in a manner enabling thermal variation of the volume of the space between the panes by deformation of the spring strip in a uniform piston-like manner. The spring strip tends to bulge outwardly when the space is filled with gas under pressure and the pane is pressed outwardly by the pressure differential thereacross. The spring strip thus tends to limit or avoid bulging of the glass or any deformation thereof.
While such window units have been found to have some insulating capacity, they do not have a significant acoustic damping effect, i.e. they do not attenuate sound transmission through the window structure to a sufficiently high degree. For instance, when the width of the spacing between the inner and outer panes is about 10 mm, a common dimension, the sound transmission attenuation is in the range of 20 to 30 decibels (dB).
It is possible, with structural complications, to increase the spacing between the inner and outer panes to a value of, say, 100 mm and thereby to increase the mean attenuation of sound transmission through the window structure, i.e. the sound damping to about 38 to 40 dB.
It is difficult, if not impossible, with conventional thicknesses, reasonable spacings of the two glass panes and an overall thickness of the structure of 70 to 80 mm to achieve an acoustic damping in excess of 42 dB.